The present invention relates to an alarm message generation system for generating and broadcasting an alarm message in the event of an alarm event and, more particularly, to such a system wherein the integrity of the system is supervised by supervising the alarm message itself rather than a superimposed supervision signal.
Fire and security alarm reporting systems which provide local and/or remote alarms upon the occurrence of fires or breaches in security require supervision of the alarm reporting system to prove the integrity of that system so that assurance will be given that, when a fire or a breach of security occurs, the proper alarm will be generated and broadcast. Prior art supervisory systems have usually involved superimposing a signal upon the alarm reporting system and sensing for the presence of that signal in order to ensure the integrity of the alarm reporting system itself. Thus, if the superimposed supervisory signal passes through the alarm generating and broadcast system properly, then it follows that the alarm message itself will pass through the system properly when an alarm event occurs.
Supervising the integrity of an alarm reporting system by superimposing a signal upon the system and sensing for that signal has several drawbacks. Such a supervisory technique requires a generator for the supervisory signal in addition to the alarm signal generator. Furthermore, special care must be taken to select those electronic alarm reporting system components which are frequency compatible with both the frequency of the alarm signal to be broadcast in the case of an alarm condition and the frequency of the superimposed supervisory signal. This latter requirement imposes restrictions upon component selection which can increase the cost and complexity of the system.